In a manufacturing line for electric resistance welded pipes, a steel plate passes through a cutter called an edge trimmer for a uniform width of the steel plate and then enters a forming unit. Examples of such an edge trimmer include a helical blade cutter described in patent literature 1.
As shown in FIG. 13, the helical blade cutter is provided with multiple linear blades 20 attached to an outer circumferential surface of a round body 10 having an outer surface formed into a cylindrical circumferential surface and arranged at given intervals in a circumferential direction, specifically in a rotational direction X. Each blade 20 is formed by aligning multiple cutting chips 21 in a straight line from one end side toward an opposite end side of the round body 10 in a direction of a rotational central axis. Each blade 20 tilts back to an angle α from a straight line P on the outer circumferential surface parallel to the rotational central axis O to be behind the straight line P in the rotational direction X. The backward tilt angle α is called a helix angle α in an axial direction. The blade 20, a chip holder 30, and a wedge-shaped chip fixing member 40 are inserted and fixed together in each of multiple cuts 12 like slits that are formed diagonally in the outer circumferential surface of the round body 10 at a tilt angle same as the helix angle α.
More specifically, recessed arcuate surfaces 11 are formed in the outer circumferential surface of the round body 10 that tilt from the straight line P on the outer circumferential surface parallel to the rotational central axis O to an angle same as the helix angle α and arranged at given intervals in the circumferential direction. The cut 12 like a slit is formed to extend from a part between adjacent ones of the arcuate surfaces 11, 11 toward one of the arcuate surfaces 11 ahead of the other in the rotational direction. As shown in FIG. 14, the multiple cutting chips 21 forming the blade 20 and held by the chip holder 30 are fitted in each cut 12 substantially completely. Multiple wedge-shaped chip holding members 40 provided for the corresponding cutting chips 21 and fitted in each cut 12 in places ahead of these cutting chips 21 and the chip holder 30 in the rotational direction are screw fixed to the bottom surface of this cut 12, thereby fixing the multiple cutting chips 21 and the chip holder 30 together in the cut 12.
The linear blade 20 held in the cut 12 in the round body 10 tilts back to an angle β from a radial line R of the round body 10 to be behind the radial line R in the rotational direction X. The backward tilt angle β is called a rake angle β in a negative direction relative to the radial line R (hereinafter simply called a rake angle β). The backward tilt angle β is the same as a tilt angle in a direction of an elevation angle from a tangent T to the outer circumferential surface of the round body 10, specifically an elevation angle. To form a swarf pocket, the upper surface of the wedge-shaped chip fixing member 40 is an arcuate surface continuous with the arcuate surface 11 of the round body 10.
For operation of the aforementioned helical blade cutter, the helical blade cutter is rotated with the rotational central axis tilting forward in a direction opposite the direction of the tilt of the blade 20. More specifically, the rotational central axis O tilts forward in a traveling direction of a steel strip to an angle γ approximate to the helix angle α. This makes the blade 20 tilting back in the traveling direction of the steel strip to the helix angle α abut on an edge of the steel strip with a slight backward tilt angle (α-γ) (see FIG. 4). The rotational direction X of the helical blade cutter is the same as a traveling direction Y of the steel strip. Further, the helical blade cutter is rotated at a speed higher than a traveling speed of the steel strip. As a result of this difference in speed, the edge of the steel strip is cut. The helix angle α and the rake angle β in the axial direction are requisites for cutting the edge at right angles and flattening the edge.
The helical blade cutter has many characteristics. Some of these characteristics are listed as follows. The blade 20 has the given helix angle α and rake angle β and abuts on an edge portion of the steel strip with backward tilt angles in two directions (angle (α-γ) and rake angle β). This achieves smooth sawing while controlling cutting to a relatively short distance. This reduces a load on each cutting chip 21 of the blade 20. Further, a cutting arc at the edge portion becomes an ellipse to reduce a maximum thickness of a swarf. The load on the cutting chip 21 is further reduced in this regard. With attention placed on one blade 20, a cutting position moves sequentially in a manner that depends on a cutting margin. This suppresses temperature increase of the cutting chip 21 to allow the multiple cutting chips 21 to wear uniformly. In this regard, reduction in the load on the cutting chip 21 can also be expected.
As described above, the helical blade cutter characteristically reduces a load on the blade 20 and a load on each cutting chip 21 forming the blade 20. However, using the helical blade cutter as the aforementioned edge trimmer brings the following problems.
The helical blade cutter is generally caused to follow displacement of a steel plate in a width direction by an edge portion detecting sensor or a copying machine so as to maintain contact between the blade 20 and an edge portion of the stele plate at a level substantially the same as an original cutting margin. If a rapid change in the circumstance of a material is caused, for example, if large camber of the steel plate occurs or the width of the steel plate changes, the edge portion of the steel plate may collide with the cutting chip 21 forming the blade 20. This might damage the cutting chip 21 or the chip holder 30.
A holder retainer 18 is provided behind the chip holder 30 in the rotational direction. The holder retainer 18 is located in a place between adjacent ones of the arcuate surfaces 11, 11. The holder retainer 18 is inherently thin for the presence of the cut 12. Additionally, for the presence of the arcuate surface 11 behind the holder retainer 18 in the rotational direction, the holder retainer 18 becomes thinner in response to approach toward its outer circumferential portion (tip portion). For this reason, damage on the chip holder 30 damages the holder retainer 18 easily. More specifically, the tip portion is broken and a base portion is bent.
The round body 10 is made of a material of high rigidity subjected to heat treatment such as quenching. Thus, the round body 10 cannot be repaired easily by means such as hardfacing and cannot undergo treatment easily for repairing the bend. For this reason, damage even on a part of the round body 10 inevitably necessitates disposal and exchange of the round body 10 in its entirety. The round body 10 entails high material cost. Additionally, the round body 10 involves complicated processing and entails extremely high processing cost for its three-dimensional shape with a large number of the arcuate surfaces 11 and a large number of the cuts 12 formed in the surface of the round body 10 and having tilts in two directions on the circumferential surface. The round body 10 further entails cost for subsequent heat treatment. For these reasons, the round body 10 is a considerably costly product so disposal and exchange of the round body 10 leads to a large economical loss.
If damage on the cutting chip 21 does not extend to the holder retainer 18 of the round body 10 but it damages only the cutting chip 21 or the chip holder 30, the cutting chip 21 or the chip holder 30 is to be exchanged. This exchange involves burdensome manual operation inside the cut 12 including detachment of the chip fixing member 40. Attaching the blade 20 for producing a new helical blade cutter is also burdensome operation as it should be done inside the cut 12.